I'm pretty sure I can put a 6 bolt 440 crank in the block with no major machining. I am aware I can get a 440 but I am trying to keep my dart somewhat unique. A 413 could be more exciting then my tiny street 318.
When I sold my 354 I also wanted something unique after having unique . I had looked at the 413's I knew their race history and with the cross rams produced tons of torque . Through my research and talking with old builders , the 413 is really quite limited and as was stated pistons if found are costly . If you want unique I would try and find a 383 RB not many made and hard to come by but parts are available and inner changeable .